An authentication system includes: a portable electronic device (for example, a mobile telephone device), into which a passcode is input; and a reader for determining whether the passcode transmitted from the mobile telephone device coincides with a pre-registered passcode, and in a case in which the passcodes coincide with each other, a key provided to a door is unlocked.
In a mobile telephone device in an authentication system disclosed in Patent Document 1, communication with a reader is performed in advance, an identifying signal is transmitted to the reader, a response to the identifying signal thus transmitted is received from the reader, and subsequently, a user operates a key operation unit to input a passcode, and the passcode thus input is transmitted to the reader.
Moreover, in a mobile telephone device in an authentication system disclosed in Patent Document 2, transmission and reception of signals with a reader are repeated for transitioning to a mode for inputting a passcode. In the mobile telephone device that transitioned to such a mode, a passcode is input by a user operating a key operation unit, and identification (ID) information and the passcode thus input are transmitted to a reader. In this case, the passcode and the ID information transmitted from the mobile telephone device are cross-checked by the reader with a pre-registered passcode and ID information, respectively, and in a case in which both of them coincide with each other, a key is unlocked.    Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2002-339608    Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2001-193324